the horns in most of the synths are crap. They sound too midi for anything realistic.
The better way is to look into the horn Specific packages that are available. The ones with articulation that mimics real players. Those are the better sounding ones, but they are not cheap. I can't recommend any specific one because I generally do not use horn in my music so it's not something I am very familiar with.
Google search for horn and brass synths and you will find a number of packages.....some are instrument specific...such as SAX only or TRUMPET only.... others are full brass sections and are aimed at a specif genre..... so look around on the net.
I use Band in a Box but.... the downside to band in a box is that you can not tell it what to play...as in a specific melody. this is an example of BB horns in a tune>>>
http://www.soundclick.com...134&songID=9012413 Articulation is pretty good but the melody is more of a jam...... it works great for fills and jamable stuff.... not so much if the horns need to play the melody.